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  2. Dolch word list - Wikipedia

    en.wikipedia.org/wiki/Dolch_word_list

    Dolch compiled the list based on children's books of his era, which is why nouns such as "kitty" and "Santa Claus" appear on the list instead of more current high-frequency words. The list contains 220 "service words" that Dolch thought should be easily recognized in order to achieve reading fluency in the English language.

  3. Sight word - Wikipedia

    en.wikipedia.org/wiki/Sight_word

    e. High frequency sight words (also known simply as sight words) are commonly used words that young children are encouraged to memorize as a whole by sight, so that they can automatically recognize these words in print without having to use any strategies to decode. [1] Sight words were introduced after whole language (a similar method) fell ...

  4. Radio spectrum - Wikipedia

    en.wikipedia.org/wiki/Radio_spectrum

    The radio spectrum is the part of the electromagnetic spectrum with frequencies from 3 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particularly in telecommunication. To prevent interference between different users, the generation and transmission of radio ...

  5. Emergency position-indicating radiobeacon - Wikipedia

    en.wikipedia.org/wiki/Emergency_position...

    121.5 MHz VHF ± 6 kHz (frequency band protected to ±50 kHz) [64] (Satellite detection ceased on 1 February 2009, [65] but this frequency is still used for short-range location during a search and rescue operation) 243.0 MHz UHF ± 12 kHz (frequency band protected to ± 100 kHz) [64] [66] (prior to 1 February 2009 – COSPAS-SARSAT Compatible)

  6. Electromagnetic spectrum - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_spectrum

    In frequency (and thus energy), UV rays sit between the violet end of the visible spectrum and the X-ray range. The UV wavelength spectrum ranges from 399 nm to 10 nm and is divided into 3 sections: UVA, UVB, and UVC. UV is the lowest energy range energetic enough to ionize atoms, separating electrons from them, and thus causing chemical reactions.

  7. Line-of-sight propagation - Wikipedia

    en.wikipedia.org/wiki/Line-of-sight_propagation

    Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave propagation which means waves can only travel in a direct visual path from the source to the receiver without obstacles. [1] Electromagnetic transmission includes light emissions traveling in a straight line. The rays or waves may be diffracted ...

  8. Optical communication - Wikipedia

    en.wikipedia.org/wiki/Optical_communication

    A replica of a Chappe telegraph tower (18th century). A 'semaphore telegraph', also called a 'semaphore line', 'optical telegraph', 'shutter telegraph chain', 'Chappe telegraph', or 'Napoleonic semaphore', is a system used for conveying information by means of visual signals, using towers with pivoting arms or shutters, also known as blades or paddles.

  9. Fresnel zone - Wikipedia

    en.wikipedia.org/wiki/Fresnel_zone

    In order to ensure limited interference, such transmission paths are designed with a certain clearance distance determined by a Fresnel-zone analysis. The dependence on the interference on clearance is the cause of the picket-fencing effect when either the radio transmitter or receiver is moving, and the high and low signal strength zones are ...

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